The invention concerns automatic operating height control for the gatherer portion of a harvester header and, more particularly, control for a gatherer or platform which may pivot or oscillate in relation to the harvester body in a generally upright transverse plane.
In conventional harvesters, the gatherer or cutting platform is part of a header which is carried ahead of the combine body. Operating height is adjusted by pivoting the header about a fixed transverse axis by means of a pair of hydraulic lift cylinders. Operating height may be controlled manually or automatically but at any given height setting, the gatherer is fixed in relation to the harvester body and its lateral tilt or inclination in an upright transverse plane will be determined or gauged by the harvester drive wheels, spaced typically eight or ten feet behind the gatherer. Usually, the gatherer length is much greater than the harvester wheel spacing and so the remoteness of the harvester wheels, especially from the lateral extremities of the gatherer, makes them unreliable as a gauging means. The combination of uneven ground and variations in the combine structure including, for example, tire pressure, can easily result in an undesirable lateral tilt and an unacceptable difference in effective operating height between one end of the gatherer and the other. This is especially undesirable in a wide platform when harvesting crops such as soybeans when, to minimize crop loss, the cutterbar must be set close to the ground. This problem is common to both regular or level land combines and the conventional hillside combine. In the latter, the harvester body may be maintained automatically level with respect to sloping terrain, but the drive axle (front wheels), conforming to the ground surface behind the gatherer, still determines the lateral tilt attitude adopted by the gatherer with respect to the ground surface.
Given the continuing advances in specific capacity of combine separators and cleaning arrangements and the introduction of automatic controls extending operator capability, harvester working rate is still too frequently limited by gatherer capacity and particularly by the gatherer width factor. Thus, there is a strong and continuing interest for improving the lateral tilt control of gatherers so as to make possible more precise control, and hence, improved efficiency of operation, and particularly to make efficient use of wider platforms more feasible.
It is well known, of course, to transfer the gauging of a harvester gatherer from the harvester body wheels to the gatherer itself, mounting the gatherer so that it may float vertically and tilt or oscillate in a transverse upright plane. Skid shoes are placed on the gatherer to gauge and control operating height at one or more points along the length of the gatherer. In more recent years, as the need for wider combine harvester gatherers has developed, there have been attempts to apply this passive lateral floating solution to the field of combine harvester gatherers. For example, Izakson, in U.S. Pat. No. 3,675,404, discloses a combine cutting platform pivoted on a ball joint and counterbalanced so that he may rely on ground-engaging skid shoes to maintain the cutting platform approximately parallel to the ground. Where ground levels and contours change rapidly, the high inertia and resistance to lateral pivoting movement of extremely wide platforms places undesirable operational limitations on this approach. Basham, in U.S. Pat. No. 4,266,395, discloses a cutting platform pivoted to a feederhouse for pivoting about a fore-and-aft longitudinal axis but uses a manually controlled hydraulic cylinder rather than ground-engaging shoes for control. Effective use of this arrangement may place unacceptable additional demands on the gcombine operator's skill and concentration.
A further disadvantage of the lateral tilt control improvements offered by Basham and others is the requirement for an adapter frame or box between the feederhouse and the gatherer platform. In some cases, this spaces the delivery point of the gatherer conveyor so far from the reception point of the feederhouse conveyor that an intermediate conveyor element, such as a transverse horizontally rotating beater, must be introduced, adding undesirably to cost, weight and complexity of the header arrangement.
Another possible solution to the problem of wide platform control is exemplified by Kejr (U.S. Pat. No. 4,487,004). The platform is split into two or more sections hinged together about generally fore-and-aft axes so that the platform may flex to follow ground surface contours, possibly assisted by automatic height control means.
A recent improvement proposed by Hart-Carter (Field Tracker sales folder 1984) adds automatic lateral tilt control in a structure similar to Basham's. An adapter box between the conventional feederhouse and cutting platform provides a fore-and-aft pivot beneath the lower end of the feederhouse and an intermediate feeder beater between the gatherer and feederhouse. Oscillation about this pivot is controlled by a single hydraulic cylinder above the feederhouse. Height of the gatherer above the ground is sensed by a pair of sensors, one at each end of the gatherer and each driving a potentiometer. Signals from the potentiometers are compared by a microprocessor to provide a tilt control for maintaining equal height at the sensed extremities of the gatherer. A disadvantage of this arrangement is that it senses at only two points towards the opposite extremities of the gatherer and takes no account of ground surface variations along its length. This limits the preciseness of control of means operating height at the particularly, if applied to a wide rigid platform, raises the risk of running intermediate portions of the gatherer into the ground.
The conventional floating flexible cutterbar of a combine cutting platform, with or without automatic height control, is designed to conform to field surface contour and is particularly useful in harvesting soybeans where it is necessary to operate with the cutterbar as close to the ground as possible to minimize crop loss. Without automatic height control, the flexibility of the cutterbar gives it an inherent, limited capability to compensate for platform lateral tilt. However, in general, the float range so far found feasible for the flexible cutterbar is substantially less than the desirable range indicated by the degree of lateral tilt to which gatherers are frequently subjected. In some of the known flexible cutterbar arrangements with automatic height control, height sensors are spaced along the length of the cutterbar. However, the control and sensing system is unable to discriminate between height variations in general and effective lateral tilt of the gatherer. The system is always controlled by the sensor at the position on the cutterbar closest to the ground so that a substantial lateral tilt of the platform will cause a sensor close to the low end of the platform to generate a raise signal, the response to which is to raise the whole platform as a body rather than correct the tilt.